Some effects of electric vs. magnetic field Mur absorbing boundaries on FDTD RCS calculations for dielectric and magnetic scatterers

Recent calculations made for magnetic material scatters have shown that the Mur absorbing boundary condition plays a significant role in the RCS (radar cross section) calculation accuracy, and that changing from a Mur condition that operates on electric field to one operating on magnetic field may improve the accuracy of the RCS results when the composition of the scattering object is changed. To illustrate this, scattering from a 20 cm radius lossy dielectric sphere and then from a sphere composed of the dual magnetic material is considered. By duality the far zone scattering cross sections for the two should be identical. In order for the FDTD (finite-difference-time-domain) results to be exactly dual. the Mur absorbing boundary must be changed from operating on the electric field to operating on the magnetic field. However, changing from electric to magnetic field Mur conditions causes the scattering results to differ by as much is 6 dB.<>